Terry Hatfield
05-09-2003, 2:54 AM
Several folks have emailed me wanting to know exactly how blower curves are created and how the tests are done in general so I thought I would just post the information.
Testing is done using a Dwyer 2010AV0-10 magnehelic gauge and 167-6 pitot tube(you can see it in the pic on the bench). The magnehelic gauge measures the static pressure and the feet per minute of duct speed. The pitot tube is intalled in the pipe 24" from the inlet centered in the diameter of the pipe. The fpm measurment is multiplied by the area of the duct (.196 for 6"). Example: If your duct speed is 5000 fpm in a 6" duct, you simply multiply 5000 X .196 to get....980 cfm.
A regular clamp on style ammeter is used to measure the amperage of the motor at each sp level.
A 72" long, 6" diameter test pipe is used. The length is sized for the particular duct diameter as per Dwyers instructions. If you were testing 10" ducts, your test pipe would have to be 12' long!!! A disc is installed on the end of the test pipe to prevent the air from flowing down the pipe and making a sharp 180 at the end. This would create turbulents in the pipe.
I built a cone shaped needle valve so I could get exact sp readings...exactly 4sp, 5sp,6sp and so on. The test pipe is completely blocked to measure the maximum sp. That is why there is no cfm number for the max sp...there is no air moving. The cone is mounted on a piece of all thread that goes through a mdf box. There is a handle on the back so I can just screw it in and out.
I should not give away my secrets...but...the cone on the needle valve is made from the reflector on an elcheapo clip on light I bought at Lowes. The cone shape of the valve smooths the air entering the test pipe and reduces turbulents so the test numbers are more accurate.
We begin with the test pipe wide open and use the valve to inccrease the sp 1" at a time until it is completely blocked to figure the complete blower curve.
Hope that answers the questions.
Thanks,
Terry
Testing is done using a Dwyer 2010AV0-10 magnehelic gauge and 167-6 pitot tube(you can see it in the pic on the bench). The magnehelic gauge measures the static pressure and the feet per minute of duct speed. The pitot tube is intalled in the pipe 24" from the inlet centered in the diameter of the pipe. The fpm measurment is multiplied by the area of the duct (.196 for 6"). Example: If your duct speed is 5000 fpm in a 6" duct, you simply multiply 5000 X .196 to get....980 cfm.
A regular clamp on style ammeter is used to measure the amperage of the motor at each sp level.
A 72" long, 6" diameter test pipe is used. The length is sized for the particular duct diameter as per Dwyers instructions. If you were testing 10" ducts, your test pipe would have to be 12' long!!! A disc is installed on the end of the test pipe to prevent the air from flowing down the pipe and making a sharp 180 at the end. This would create turbulents in the pipe.
I built a cone shaped needle valve so I could get exact sp readings...exactly 4sp, 5sp,6sp and so on. The test pipe is completely blocked to measure the maximum sp. That is why there is no cfm number for the max sp...there is no air moving. The cone is mounted on a piece of all thread that goes through a mdf box. There is a handle on the back so I can just screw it in and out.
I should not give away my secrets...but...the cone on the needle valve is made from the reflector on an elcheapo clip on light I bought at Lowes. The cone shape of the valve smooths the air entering the test pipe and reduces turbulents so the test numbers are more accurate.
We begin with the test pipe wide open and use the valve to inccrease the sp 1" at a time until it is completely blocked to figure the complete blower curve.
Hope that answers the questions.
Thanks,
Terry